Shimano Positron: How old ?

Jacques Moser said:

Hello everybody,

I just bought a very cheap bike that I can leave at the station. It has a
7-speed derailleur labelled "Positron FH400", actioned by a handlebar
lever labelled "PPS Shimano". The system provides a somewhat crude
indexing, which is handled by the derailleur, not by the lever.

I am puzzled about how old this bike can be: Fenders and rims are steel,
but can a 7-speed indexed der be that old ? Any ideas ?

You have one of Shimano's many failed Big Ideas there (add oversize
pedal threads, the amusingly acronymed Front Freewheel System, U-brakes,
Biopace and probably soon Octalink bottom brackets). Anyway, Positron
dates from 1977 and was laid to rest before 1984.

Jacques Moser said:

Quoted message said:

Hello everybody,

I just bought a very cheap bike that I can leave at the station. It has a
7-speed derailleur labelled "Positron FH400", actioned by a handlebar
lever labelled "PPS Shimano". The system provides a somewhat crude
indexing, which is handled by the derailleur, not by the lever.

I am puzzled about how old this bike can be: Fenders and rims are steel,
but can a 7-speed indexed der be that old ? Any ideas ?

Zog did not deny:

Quoted message said:

You have one of Shimano's many failed Big Ideas there (add oversize
pedal threads, the amusingly acronymed Front Freewheel System, U-brakes,
Biopace and probably soon Octalink bottom brackets).

The "Dyna Drive" pedals, with the bearings inside the threads of the
oversized crank were actually a rather good idea. I never heard of any
of these cranks breaking at the pedal eye, unlike standard cranks.

The offered an arguably real biomechanical advantage, but failed mainly
because the bearings couldn't hold up to the stress.

"U brakes" were originally offered as a simpler alternative to the
excessively complicated rollercam brakes that were in vogue in the mid
'80s. Rollercams are now extinct, but U brakes are still in production
(though not by Shimano) as they remain popular for BMX/Freestyle
applications.

U brakes are the best choice for a brake that must be mounted below the
chainstays, because it avoids crank clearance problems. Mounting the
brakes down there was a silly cosmetic fad for mtbs in the mid '80s,
(not a fad that Shimano started...SunTour was more guilty of that.)

Biopace was a commercial failure, but a technical success, in my
opinion, and I still prefer it over round chainrings.

See: http://sheldonbrown.com/biopace

Quoted message said:

Anyway, Positron dates from 1977 and was laid to rest before 1984.

That's true in the U.S. market, but it remained semi-popular in Europe
for quite a while after that. When I lived in France, 1988-89,
Positron-equipped town bikes were offered in every sizable bike shop I
visited. I had the impression that they were more popular in West
Germany than they were in France.

Positron was the first commercially successful indexed derailer system.

Sheldon "Histoire" Brown
+-------------------------------------------------------+
| ...what is hailed as a new style or a new school |
| in literature often consists of doing as a novelty |
| what a Victorian did long ago as a joke. |
| -- G.K. Chesterton |
+-------------------------------------------------------+
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I suppose Syncro 1 & Syncro 2 were good ideas?

begin quoting Sheldon Brown <[email hidden]>:

Quoted message said:

The "Dyna Drive" pedals, with the bearings inside the threads of the
oversized crank were actually a rather good idea. I never heard of any
of these cranks breaking at the pedal eye, unlike standard cranks.
The offered an arguably real biomechanical advantage, but failed mainly
because the bearings couldn't hold up to the stress.

Perhaps, then, they didn't break at the pedal eye because no-one had them
in service long enough?
--
David Damerell <[email hidden]> Distortion Field!
Today is Chedday, January.

Sheldon Brown said:

The "Dyna Drive" pedals, with the bearings inside the threads of the
oversized crank were actually a rather good idea. I never heard of any
of these cranks breaking at the pedal eye, unlike standard cranks.

I'm sorry to tell you that I have (my friend Gareth, early 1990s).